# Standard deviation in numpy

## Question:

Here is my code:

```
import numpy as np
print(np.std(np.array([0,1])))
```

it produces `0.5`

I am confident that this is incorrect. What am I doing wrong?

## Answers:

By default, `numpy.std`

returns the population standard deviation, in which case `np.std([0,1])`

is correctly reported to be `0.5`

. If you are looking for the sample standard deviation, you can supply an optional `ddof`

parameter to `std()`

:

```
>>> np.std([0, 1], ddof=1)
0.70710678118654757
```

`ddof`

modifies the divisor of the sum of the squares of the samples-minus-mean. The divisor is `N - ddof`

, where the default `ddof`

is `0`

as you can see from your result.